[Nut-upsuser] Purpose of LOGIN and LOGOUT

[Roger Price]

On Fri, 21 Feb 2020, Mark McMillan wrote:

> What is the purpose of the LOGIN <upsdevice> and LOGOUT commands in the 
> network protocol?

According to section 9.9 at 
https://networkupstools.org/docs/developer-guide.chunked/ar01s09.html :
<< Use this to log the fact that a system is drawing power from this UPS. The 
upsmon master will wait until the count of attached systems reaches 1 - itself. 
This allows the slaves to shut down first. >>

> It seems if I supply USERNAME and PASSWORD then I am able to perform any 
> operations on the device, so why would I need to use LOGIN?

The USENAME and PASSWORD are used for the LOGIN which gives access to upsd's 
status change reports.

> And since LOGIN takes a <upsdevice> but LOGOUT does not, I guess that LOGOUT 
> is implicitly associated with the last (most recent) LOGIN?

> Which means a single client cannot be logged into more than one device at a 
> time?

If by "client" you mean a single MONITOR declaration in upsmon.conf then that 
corresponds to just one LOGIN.  But upsmon.conf may have multiple MONITOR 
declarations with multiple LOGINs.  Additionally, multiple upsmon instances may 
have MONITOR declarations corresponding to the same device, as in the system I 
use to type this note.

Roger